1. Field of the Invention
The present invention relates to an apparatus for making tissue. More specifically, the present invention relates to means for adjusting the angle defined between a doctor and a peripheral surface of a Yankee dryer for controlling the physical dimensions of microfolds generated during peeling of the tissue from the Yankee dryer.
2. Information Disclosure Statement
In the manufacture of tissue paper grades, the tissue is creped from a Yankee dryer by means of a doctor. Such creping generates a series of microfolds, or macrofolds, which are formed in the sheet in order to attain the optimal level of stretch for converting and softness for quality.
The tissue sheet is typically peeled off the Yankee dryer by the use of a steel or ceramic blade. The angle at which the aforementioned blade or crepe doctor is set at greatly impacts the crepe quality of the sheet. The highest crepe quality is attained by putting the smallest length microfolds into the sheet at high frequency and by assuring a level crepe profile across the width of the tissue sheet coming to the reel downstream relative to the Yankee dryer.
Control of creping normally requires time-consuming, difficult changes to the doctor holder and conforming types of holders. Until recently, operators did not have the means for adjusting the crepe angle as the crepe blade wore down. Consequently, as the blade wears, the crepe angle changes. Subsequently, as the blade angle changes, so does the quality of crepe generated in the sheet. Since Yankee doctor blades are typically changed once or twice during a shift during normal operation, it is clearly evident that tissue sheet quality changes frequently during the course of a day.
A recent modification to a Yankee doctor allows for on-the-run manual adjustment of the crepe doctor angle. However, tissue quality measurements are time-consuming, and adjustments of the crepe angle is frequently late and inaccurate. Moreover, the adjustments are still done manually, which requires operator attention in a dusty environment.
The present invention solves the aforementioned problem by adding a device that is able to read crepe in the tissue sheet. Such is done by measuring both the length and the height of each microfold. The device, according to the present invention, is able to work at a single location, or alternatively, to traverse across the width of the tissue paper machine. The apparatus, according to the present invention, permits the transmittal of information to a control unit. The control unit houses an algorithm that controls the crepe angle. The control unit is also capable of transmitting information to an adjustable angle crepe doctor. Upon receiving the signal from the control unit, the crepe angle will be changed instantaneously to adjust for process changes, such as blade wear, furnish changes, uneven Yankee coating, uneven moisture profile and a myriad of other changes which impact crepe uniformity and quality.
The present invention is designed to run in closed loop mode but will also be capable of running with manual adjustments. Since information on crepe uniformity and crepe quality are instantaneously available, the operator of the apparatus will be able to make more timely manual adjustments to the adjustable angle crepe doctor.
Therefore, it is a primary objective of the present invention to provide an apparatus which permits automatic control of the angle of a doctor so that the physical dimensions of the generated microfolds is optimized.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.